1. Field of the Invention
The invention relates generally to dimensionally unstable layers, such as but not limited to photoresist layers, used for fabricating microelectronic structures. More particularly, the invention relates to patterned dimensionally unstable layers, such as patterned photoresist layers, used for fabricating microelectronic structures.
2. Description of the Related Art
Microelectronic structures are typically fabricated over substrates while using patterned photoresist layers as mask layers. The patterned photoresist layers typically mask portions of a substrate, frequently but not exclusively a semiconductor substrate, to allow for regioselective processing of other portions of the substrate. Non-limiting examples of regioselective processing include etch processing, deposition processing, plasma modification processing and ion implantation processing.
As microelectronic structure dimensions decrease, the dimensions of patterned photoresist layers used in their fabrication clearly must also decrease. In turn, as the dimensions of patterned photoresist layers decrease, a wavelength of energy needed for their photoexposure similarly also decreases. Such a decrease is generally required in order to avoid undesirable optical effects when photoexposing a blanket photoresist layer and forming a latent pattern therein. As a result, advanced photoresist materials are generally inherently more sensitive to higher energy (i.e., lower wavelength, such as, for example 193 nm) radiation sources.
One consequence of the enhanced sensitivity of advanced photoresist materials to higher energy radiation sources is that patterned photoresist layers comprised of those materials are often also inherently sensitive to higher energy radiation sources other than those used for their photoexposure. The sensitivity is often manifested as a shrinkage or dimensional variation of a patterned photoresist layer incident to exposure to higher energy radiation sources such as electron beam sources used for scanning electron microscopy linewidth measurement of the patterned photoresist layer. The shrinkage or dimensional variation may occur for patterned photoresist layers comprising various types of photoresist materials.
Typically, an absence of accurate and effective measurement of patterned photoresist layer linewidth generally leads to questionable quality control and quality assurance when fabricating microelectronic structures and devices. It may also lead to non-functional or unreliable microelectronic structures and devices.
Fortunately, methods for inhibiting shrinkage of patterned photoresist layers are known in the semiconductor fabrication art.
For example, Holscher et al., in U.S. Pat. No. 6,107,002 teaches a method for inhibiting shrinkage of a patterned photoresist layer comprising a positive photoresist material that also includes a photo-acid generator material. The method provides for photoactivating and neutralizing the photo-acid generator material prior to using the patterned photoresist layer as a reactive ion etch mask where it would otherwise shrink.
In addition, Ke et al., in U.S. Pat. No. 6,774,044, teaches a method for dimensionally stabilizing a patterned photoresist layer to inhibit shrinkage thereof incident to a scanning electron microscopy linewidth measurement thereof. The method provides for a plasma treatment of the patterned photoresist layer prior to the scanning electron microscopy linewidth measurement thereof.
Notwithstanding the foregoing disclosure, under certain alternative circumstances curing of a patterned photoresist layer using a plasma may induce a linewidth shrinkage during a curing process.
Also known in the semiconductor fabrication art are photoresist test structures that may be used incident to semiconductor device manufacturing and quality assurance.
In particular, Seniuk et al., in U.S. Pat. No. 6,635,405 teaches a patterned photoresist layer test structure that allows for decoupling of processing effects such as overexposure effects, underexposure effects and depth of focus effects. The test structure comprises a series of dimensionally progressing patterned photoresist layer dots and a correlating and complementary series of dimensionally progressing holes within an additional patterned photoresist layer.
Microelectronic structure dimensions and patterned photoresist layer dimensions are certain to decrease, and as a result thereof patterned photoresist layer sensitivity to higher energy radiation sources is also likely to increase. Desirable are structures and methods that allow for accurate determination of patterned photoresist layer dimensions in spite of dimensional sensitivity of patterned photoresist, layers to higher energy radiation sources.